Power semiconductors are used as switches or rectifiers in certain power electronics, such as switch-mode power supplies. They are also called power devices or, when used in integrated circuits, power integrated circuits (ICs). A power semiconductor is usually used in commutation mode (it is either on or off), and has a design optimized for such usage. Power semiconductors are found in systems delivering tens of milliwatts (e.g., a headphone amplifier) and in systems delivering a gigawatt (e.g., a high voltage direct current transmission line).
Certain metal-oxide-semiconductor field-effect transistors (MOSFETs), a type of power semiconductor, are depletion channel devices: Voltage, not current, may be necessary to create a conduction path from drain to source. At low frequencies, this can reduce gate current because it is only required to charge gate capacitance during switching. Switching times range from tens of nanoseconds to a few hundred microseconds. Typically, MOSFET devices are not bi-directional and are not reverse voltage blocking.
An insulated-gate bipolar transistor (IGBT), another type of power semiconductor, often has characteristics common to bipolar junction transistors (BJTs) and MOSFETs. It may have a high gate impedance and thus low gate current requirements like a MOSFET. It may also have a low on state voltage drop in the operating mode like a BJT. Certain IGBTs can be used to block both positive and negative voltages, and have reduced input capacitance compared to MOSFET devices.